Upon first using my pH probe, I noticed a little fleck of black in the sponge that sits in the bottom of the probe cover/cap but didn't think much of it. I came to use it the other day a couple of months after that first use and the cover is now full of what I assume is mould. What is the recommended way of cleaning this out? I know I need to change the 3M KCl but because the mould is in the sponge bit, I need to be able to clean that somehow? Thank you.